Method of producing cellulose carbamate fibre and use of the same

ABSTRACT

The invention relates to a cellulose carbamate spinning solution, cellulose fibres and a method for the production thereof in which a solution of cellulose carbamate in an ionic liquid is pressed through the holes of a spinning nozzle. The shaped fibres are stretched in air and the cellulose carbamate is regenerated in an aqueous bath. Solvent is removed by washing and the fibre is subsequently dried.

The invention relates to a cellulose carbamate spinning solution, cellulose fibres and a method for the production thereof in which a solution of cellulose carbamate in an ionic liquid is pressed through the holes of a spinning nozzle. The shaped fibres are stretched in air and the cellulose carbamate is regenerated in an aqueous bath. The solvent is removed by washing and the fibre is subsequently dried.

The production of cellulose fibres according to the viscose process is still the mostly used method (K. Götze, “Chemical Fibres According to the Viscose Method”, Springer Press, Berlin Heidelberg New York 1967). Since the viscose method is associated with significant environmental impact, e.g. due to carbon disulphide, hydrogen sulphide, heavy metals, and also with high investment costs, efforts have already been made for years to replace the viscose method by alternative methods. Methods have been developed on the basis of direct dissolving of pulp in a suitable solvent or alternative derivatisation variants without carbon disulphide.

The cuproammonium method which is based on the solubility of pulp in copper oxide ammonia solution is comparable to the viscose method from the initiation time (Ullmann's Encyclopedia of Industrial Chemistry: Cellulose—3.3 Cuprammonium Fibres).

One method (Tencel®) introduced for the production of cellulose fibres is the spinning of solutions of cellulose in amine oxides, preferably in N-methylmorpholine-N-oxide (NMMO), not least because by means of this the complex route via derivatisation of the cellulose is avoided. It is known from DE 28 30 685 and U.S. Pat. No. 3,767,756 and also EP 0 490 870 that cellulose is soluble in an NMMO water system and can be processed to form textile fibres by spinning in a generally aqueous NMMO solution

A further known possibility for the production of moulded articles made of regenerated cellulose resides in precipitating a solution of cellulose carbamate (EP 57 105, EP 178 292) which is formed by conversion of cellulose with urea. Cellulose carbamate is soluble in cold sodium hydroxide solution and can be regenerated again into cellulose in heated sodium hydroxide solution.

The low solids concentration of the cellulose in the spinning solution which is generally 8 to 15% is disadvantageous for the productivity of the described cellulose wet spinning methods.

The use of concentrations above 20% for the production of cellulose fibres on the basis of extrusion of solutions of cellulose carbamate in NMMO is described in DE 10 2004 007 616. In this method, the high spinning solution viscosities have a disadvantageous effect. The spinning solution production is effected by swelling the cellulose carbamate in a 40 to 70% NMMO/water mixture and subsequent distilling-off of water, which demands significant dissolving times and a fairly high energy requirement.

Ionic liquids have been described as a further solvent for cellulose in recent times. Ionic liquids are salts which are constructed from a cyclic, generally nitrogen-containing cation and an organic or inorganic anion and have a melting point below 100° C. Possibilities for synthesis of ionic liquids, the use as medium in chemical reactions and also as solvents for cellulose and also the formation of these solutions into fibres are described in the subsequently mentioned publication (G. Laus, G. Bentivoglio, H. Schottenberger, V. Kahlenberg, H. Kopacka, T. Röder, H. Sixta, “Ionic Liquids: Current Developments, Potential and Drawbacks for Industrial Applications” in Lenzinger Berichte, 84 (2005) 71-85).

In WO 2006/000197, a method and device for the production of moulded articles from solutions of cellulose in ionic liquids are described. The pulps are disintegrated here in water and supplied to the dissolving process in wet form. This means that the water must be removed during dissolving, as a result of which the dissolving time and the energy requirement are affected. The described spinning solutions with concentrations up to 20% have very high zero shear viscosities.

Starting herefrom, it was the object of the present invention to provide a cellulose carbamate spinning solution in which the cellulose carbamate is present in high concentrations in dissolved form. It was also the object of the present invention to provide, in comparison with existing methods, an environmentally friendly method for the production of qualitatively high-quality cellulose fibres, which method fulfils the demands with respect to low investment and production costs due to high solution concentrations. A further object of the invention was to indicate a correspondingly produced fibre and also possibilities for using the fibre.

This object is achieved with respect to the cellulose carbamate spinning solution by the features of patent claim 1, with respect to the method for the production of spun cellulose carbamate fibres by the features of patent claim 10, with respect to the cellulose carbamate fibres by the features of patent claim 16 and also with respect to the possibilities for using the fibres by the features of patent claim 20 and 21. The respective dependent claims demonstrate advantageous developments.

According to the invention, a spinning solution made of cellulose carbamate is hence provided, the cellulose carbamate being dissolved in at least one ionic liquid. According to the invention, the cellulose carbamate concentration of the spinning solution is thereby at least 15% by weight and the zero shear viscosity, measured at 100° C., is thereby in a range of 50 to 7,500 Pas.

It was shown surprisingly that cellulose carbamate dissolves in ionic liquids up to high concentrations and can be shaped to form fibres with high strengths. It was likewise shown surprisingly that the highly-concentrated solutions, compared to cellulose in ionic liquids and also to cellulose carbamate in NMMO, have far lower zero shear viscosities at the processing temperature.

For the production of the spinning solution according to the invention, cellulose carbamate is dissolved in an ionic liquid with agitation or kneading at temperatures above 80° C. and the resulting spinning solution is filtered.

Preferably, dried cellulose carbamate is used for production of the spinning solution and the spinning solution is formed by mechanical mixing at temperatures between 80 and 120° C., preferably between 90 and 100° C. When using water-containing cellulose carbamate, the dissolving is effected by kneading with simultaneous withdrawal of the water at reduced pressure, e.g. less than 0.9 bar.

In an advantageous embodiment, the melting point of the at least one ionic liquid is below 100° C., preferably below 75° C., particularly preferred below 50° C.

The at least one ionic liquid is thereby selected preferably from the group consisting of ammonium-, pyrazolium-, cholinium-, in 1- and 3-position alkyl- or aryl-substituted imidazolium compounds and/or mixtures hereof, in particular butyl methylimidazolium acetate, butyl methylimidazolium chloride, ethyl methylimidazolium chloride, ethyl methylimidazolium acetate, butyl ethylimidazolium acetate, butyl ethylimidazolium chloride, methyl tetradecylimidazolium chloride, butyl methylimidazolium bromide, butyl methylpyridinium chloride, butyl methylimidazolium thiocyanate, ethyl methylimidazolium thiocyanate, butyl ethylimidazolium thiocyanate, hexyl dimethylimidazolium hexafluoroborate, ethoxy methyl methylpyrrolidinium chloride, hydroxypropyl methylimidazolium acetate, hydroxypropyl methylimidazolium chloride and/or butyl methylpyridinium chloride.

Further advantages are produced if the cellulose carbamate has a DP_(cuoxam) of 150 to 170, preferably of 250 to 550.

It is likewise preferred if the cellulose carbamate has a substitution degree DS_(carbamate) of 0.1 to 1, preferably of 0.2 to 0.6.

It must be emphasised as a particular advantage of the present invention that high concentrations of cellulose carbamate in solution can be set by dissolving the cellulose carbamate in an ionic liquid. The cellulose carbamate concentration can thus assume high concentration values, advantageously between 20 and 50% by weight, further preferred between 20 and 40% by weight, particularly preferred between 20 and 30% by weight.

Further advantages of the spinning solution according to the invention can be seen in the fact that, despite the high cellulose carbamate content, low zero shear viscosities are produced. Preferred ranges of the zero shear viscosity, measured at 100° C., are thereby in the range of 50 to 5,000 Pas, preferably of 150 to 2,500 Pas and particularly preferred of 250 to 1,250 Pas.

According to the invention, a method for the production of cellulose carbamate fibres is likewise provided, in which a spinning solution is pressed through a spinning nozzle which has at least one opening, the spinning solution thread formed thereby is stretched in an air gap and coagulated subsequently in a precipitation bath.

In the case of the method according to the invention, a highly concentrated solution of cellulose carbamate in an ionic liquid is hence formed by means of extrusion from a nozzle with stretching in an air gap into a coagulation bath.

Preferably, the cellulose carbamate is dissolved with agitation or kneading at temperatures above 80° C. in an ionic liquid, the resulting spinning solution is filtered and subsequently pressed through the holes of a nozzle. The resulting threads or formed items can be withdrawn at speeds of greater than 50 m/min via an air gap and a subsequent coagulation bath. In the air gap, drawing to a multiple of the original length is effected preferably and the carbamate formed item is coagulated in a coagulation bath and a part of the solvent is thereby removed. Subsequently the remaining solvent is washed out preferably in the counterflow principle and the product is dried.

Advantageously, spinning nozzles are used in the method, the 1/d ratio of which, i.e. the ratio between the length of the spinning nozzle hole to the diameter, is 2 to 20, preferably 6 to 15.

Furthermore, it is advantageous if the width of the air gap is from 5 to 250 mm.

An aqueous solution at least of one ionic liquid is used preferably as precipitation bath. It is hereby preferred if the weight concentration of the at least one ionic liquid in the aqueous solution is 0.5 to 50% by weight, preferably 2 to 25% by weight.

The temperature of the spinning solution during the spinning process is adjusted preferably to a temperature range of 50 to 150° C., preferably of 80 to 120° C. The spinning solution is thereby spun in particular according to a dry/wet jet method to form fibres.

According to the invention, cellulose carbamate fibres are likewise provided which are produced according to a previously described method. The fibres according to the invention are distinguished by very high strength.

The fibres according to the invention can be produced by varying the regeneration conditions with a varying N-content and have, as a function of the N-content, a different water absorption capacity.

The strength of cellulose carbamate fibres is in particular at least 30 cN/tex, preferably at least 50 cN/tex, measured according to DIN 53834.

Likewise, the fibres are distinguished by a high modulus of elasticity which is preferably 1,500 cN/tex, preferably at least 2,500 cN/tex.

The nitrogen content of the fibres can thereby vary preferably in a range between 0.01 and 7% by weight, preferably between 0.5 and 5% by weight.

Possibilities for use according to the invention of the cellulose carbamate fibres are thereby precursors for industrial fibres, in particular for the production of carbon fibres or reinforcing fibres for plastic materials or composites.

The subject according to the invention is intended to be explained in more detail with reference to the subsequent examples without wishing to restrict the latter to the special embodiments shown here.

Embodiments EXAMPLE 1

20 g cellulose carbamate (DPcuox: 258, DS 0.4) are mixed with 80 g butyl methylimidazolium acetate and are dissolved in a horizontal kneader at 110° C. within 2 hours. The resulting homogeneous, dark brown solution is completely fibre-free. The viscosity of the solution, measured at 100° C., is 64 Pas.

The solution was pressed by means of an extruder through a 12-hole spinning nozzle (hole diameter 150 μm), stretched with a drawing ratio of 30 in the air gap and the cellulose carbamate fibre was precipitated in the aqueous coagulation bath with 12% butyl methylimidazolium acetate. The filaments were washed with soft water and dried at 90° C.

The filaments had a strength of 52 cN/tex, a stretch of 9% and a modulus of 2,500 cN/tex.

EXAMPLE 2

30 g cellulose carbamate (DPcuox: 258, DS 0.4) are mixed with 70 g butyl methylimidazolium acetate and are dissolved in a horizontal kneader at 110° C. within 2 hours. The resulting homogeneous, dark brown solution is completely fibre-free. The viscosity of the solution, measured at 100° C., is 1,210 Pas.

The solution was pressed by means of an extruder through a 12-hole spinning nozzle (hole diameter 150 μm), stretched with a drawing ratio of 35 in the air gap and the cellulose carbamate fibre was precipitated in the aqueous coagulation bath with 15% butyl methylimidazolium acetate. The filaments were washed with soft water and dried at 90° C.

The filaments had a strength of 62 cN/tex, a stretch of 8% and a modulus of 2,970 cN/tex.

EXAMPLE 3

20 g cellulose carbamate (DPcuox: 258, DS 0.4) are mixed with 80 g butyl methylimidazolium chloride and dissolved in a horizontal kneader at 110° C. within 2 hours. The resulting homogeneous, yellowish solution is completely fibre-free. The viscosity of the solution, measured at 100° C., is 504 Pas.

The solution was pressed by means of an extruder through a 12-hole spinning nozzle (hole diameter 150 μm), stretched with a drawing ratio of 30 in the air gap and the cellulose carbamate fibre was precipitated in the aqueous coagulation bath with 12% butyl methylimidazolium chloride. The filaments were washed with soft water and dried at 90° C.

The filaments had a strength of 58 cN/tex, a stretch of 11% and a modulus of 2,400 cN/tex.

EXAMPLE 4 (COMPARATIVE EXAMPLE)

15 g of a prehydrolysis kraft pulp (DPcuox: 552) are disintegrated in water and subsequently mixed with 85 g butyl methylimidazolium acetate and dissolved in a horizontal kneader at 150 mbar at 80 to 85° C. within 3 hours. The resulting homogeneous, brown solution is fibre-free. The viscosity of the solution, measured at 100° C., is 1,649 Pas.

The solution was pressed by means of an extruder through a 12-hole spinning nozzle (hole diameter 150 μm), stretched with a drawing ratio of 30 in the air gap and the cellulose fibre was precipitated in the aqueous coagulation bath with 12% butyl methylimidazolium acetate. The filaments were washed with soft water and dried at 90° C.

The filaments had a strength of 41 cN/tex, a stretch of 9% and a modulus of 1,590 cN/tex. 

1.-9. (canceled)
 10. A method of producing spun cellulose carbamate fibres, comprising (a) pressing a spinning solution through a spinning nozzle which has at least one opening, to form a spinning solution thread, wherein the spinning solution is a cellulose carbamate spinning solution comprising a solution of cellulose carbamate in at least one ionic liquid, wherein the cellulose carbamate concentration of the spinning solution is at least 15% by weight and the zero shear viscosity, measured at 100° C., is in the range of 50 to 7,500 Pas; (b) stretching the spinning solution thread in an air gap; and (c) subsequently coagulating the spinning solution thread in a precipitation bath.
 11. The method of claim 10, wherein the 1/d ratio of the spinning nozzle is from 2 to
 20. 12. The method of claim 10, wherein the width of the air gap is from 5 to 250 mm.
 13. The method of claim 10, wherein an aqueous solution of at least one ionic liquid is used in the precipitation bath.
 14. The method of claim 13, wherein the weight concentration of the at least one ionic liquid in the aqueous solution is from 0.5 to 50% by weight.
 15. The method of claim 10, wherein the temperature of the spinning solution is from 50 to 150° C.
 16. Cellulose carbamate fibre, produced by the method of claim
 10. 17. The fibre of claim 16, wherein the fibre has a strength of at least 30 cN/tex measured according to DIN
 53834. 18. The fibre of claim 16, wherein the fibre has a modulus of elasticity of at least 1,500 cN/tex.
 19. The fibre of claim 16, wherein the fibre has a nitrogen content between 0.01 and 7% by weight.
 20. A precursor for industrial fibres comprising the fibre of claim
 16. 21. A reinforcing fibre for plastic materials or composites comprising the fibre of claim
 16. 22. The method of claim 10, wherein the ionic liquid has a melting point below 100° C.
 23. The method of claim 10, wherein the ionic liquid is selected from the group consisting of ammonium-, pyrazolium-, cholinium-, in 1- and 3-position alkyl- or aryl-substituted imidazolium compounds, and mixtures thereof.
 24. The method of claim 23, wherein the ionic liquid is selected from the group consisting of butyl methylimidazolium acetate, butyl methylimidazolium chloride, ethyl methylimidazolium chloride, ethyl methylimidazolium acetate, butyl ethylimidazolium acetate, butyl ethylimidazolium chloride, methyl tetradecylimidazolium chloride, butyl methylimidazolium bromide, butyl methylpyridinium chloride, butyl methylimidazolium thiocyanate, ethyl methylimidazolium thiocyanate, butyl ethylimidazolium thiocyanate, hexyl dimethylimidazolium hexafluoroborate, ethoxy methyl methylpyrrolidinium chloride, hydroxypropyl methylimidazolium acetate, hydroxypropyl methylimidazolium chloride, butyl methylpyridinium chloride, and mixtures thereof.
 25. The method of claim 10, wherein the cellulose carbamate has a DP_(cuoxam) of 150 to
 750. 26. The method of claim 10, wherein the cellulose carbamate has a substitution degree DS_(carbamate) of 0.1 to
 1. 27. The method of claim 10, wherein the cellulose carbamate concentration is between 20 and 50% by weight.
 28. The method of claim 10, wherein dried cellulose carbamate is used for the production of the spinning solution.
 29. The method of claim 10, wherein water-containing cellulose carbamate is used for the production of the spinning solution and the dissolving process is implemented at a reduced pressure of less than 0.9 bar.
 30. The method of claim 10, wherein the zero shear viscosity, measured at 100° C., is in the range of 50 to 5,000 Pas. 